Cooling towers are critical equipment in industrial, hospital and commercial facilities. However, they represent one of the most conducive environments for the development of Legionella pneumophila, the bacterium responsible for Legionnaires' disease. Understanding the specific risks and implementing rigorous control measures is essential to guarantee the safety of people and comply with Portuguese legislation.
How Cooling Towers Promote Legionella
Cooling towers offer ideal conditions for Legionella multiplication due to several interconnected factors.
Optimal Temperature Range The bacterium develops optimally between 20°C and 45°C. In cooling towers, water often circulates within this temperature range, particularly during the summer season, creating an environment conducive to bacterial growth.
Aerosol Formation The spray system in cooling towers disperses water droplets into the air. When contaminated with Legionella, these droplets can be inhaled by occupants of nearby buildings, representing a significant risk of infection.
Biofilm and Scale Accumulation Partial stagnation, the presence of sediments, corrosion and mineral scale create a biological film that protects the bacterium and hinders the action of biocides. This biofilm is one of the main challenges in controlling Legionella.
High Water Recirculation Continuous water recirculation increases the probability of bacterial dissemination throughout the system, significantly amplifying the risk of large-scale contamination.
Risk Assessment in Cooling Systems
A comprehensive risk assessment is the first essential step towards implementing an effective Legionella control programme.
Mandatory Inventory The entire installation must be mapped, including the identification of all cooling towers, pipework, filters and recirculation systems. This inventory documents not only the location, but also technical characteristics, water volume and maintenance operations.
Microbiological Analysis Water analysis should be carried out periodically to detect the presence of Legionella. Results indicate not only whether the pathogen is present, but also the bacterial load, allowing assessment of the effectiveness of control measures.
Identification of Critical Control Points During the assessment, the points in the system most vulnerable to bacterial growth must be identified, such as stagnation areas, zones with inadequate temperature or deteriorated components.
Control and Treatment Measures
Effective control of Legionella in cooling towers requires a multifaceted approach.
Biocide Treatment The use of specific biocidal agents (chemical or physical) is fundamental. Biocides eliminate the bacterium and help disintegrate biofilm. The choice of biocide and its concentration should be based on risk analyses specific to the facility.
Regular Purging and Maintenance Continuous purges remove sediments and reduce mineral concentration, minimising scale formation. Regular cleaning of internal surfaces reduces the potential for biofilm growth.
Temperature Control Maintaining water at temperatures above 45°C or, alternatively, below 20°C, significantly reduces the risk of Legionella. Adequate heating systems during hot water storage are crucial.
Annual Mandatory Cleaning and Disinfection Portuguese legislation requires professional deep cleaning and disinfection of the cooling tower at least once per year. This procedure removes accumulated deposits and eliminates Legionella populations that may have developed resistance to continuous treatment.
Legal Requirements Specific to Cooling Towers
Portugal, as a member of the European Union, has implemented strict regulations for Legionella control.
Decree-Law 118/2019 This legislation establishes obligations for cooling facilities, requiring those responsible to assess risks, maintain detailed records and comply with specific microbiological analysis schedules.
Mandatory Records All documentation related to Legionella control must be maintained and updated, including microbiological analyses, measurement equipment calibration, maintenance performed and treatments applied.
Frequency of Microbiological Analysis Depending on the risk assessment, analyses must be carried out at least once per month, with the possibility of increased frequency if contamination is detected.
Notification to Authorities Confirmed cases of Legionella oblige notification to the Directorate-General for Health (DGS) and, in certain cases, to the corresponding Regional Health Authority.
Conclusion
Effective control of Legionella in cooling towers is not optional—it is a legal obligation and an ethical responsibility for public health. Cooling towers are essential equipment, but they require constant vigilance, rigorous maintenance and periodic risk assessments.
If your facility includes cooling towers and does not have a structured Legionella control programme, it is time to act. The development of a Legionella Prevention and Control Plan (PPCL) tailored to your specific needs is the first step towards ensuring legal compliance and effective protection.
Contact us for a confidential risk assessment and the development of your personalised Legionella control plan.
